Extrusion die for biodegradable material with die orifice modifying device and flow control device

ABSTRACT

An extrusion die for extruding biodegradable material, the extrusion die including: a mandrel; an outer member positioned near the mandrel; an extrusion orifice between the mandrel and the outer member; a member in communication with at least one defining member of the extrusion orifice, wherein the member is capable of producing relative movement between outer member and the mandrel, wherein the relative movement has a component transverse to an extrusion direction of biodegradable material through the extrusion orifice; a flow control device which controls flow of biodegradable material through the extrusion die; and a positioning device which positions the outer member and the mandrel relative to each other. An improved process for the extrusion of biodegradable material wherein the extrusion includes flowing the biodegradable material in a flow direction through an orifice, the improvement including: moving the biodegradable material in a direction having a component transverse to the flow direction during extrusion; controlling the flow rate of biodegradable material through the extrusion die during extrusion, wherein the controlling includes adjusting the head pressure of the biodegradable material in the extrusion die and adjusting at least one cross-sectional area of a biodegradable material flow path within the extrusion die; and modifying the orifice geometry.

This is a continuation of application Ser. No. 09/035,200, filed on Mar.5, 1998, now U.S. Pat. No. 6,183,672.

BACKGROUND OF THE INVENTION

This invention relates generally to the formation of shaped objects fromexpanded biodegradable materials, and, in particular, to an extrusiondie for ultimately forming sheets of biodegradable material.

Biodegradable materials are presently in high demand for applications inpackaging materials. Commonly used polystyrene (“Styrofoam”(Trademark)), polypropylene, polyethylene, and other non-biodegradableplastic-containing packaging materials are considered detrimental to theenvironment and may present health hazards. The use of suchnon-biodegradable materials will decrease as government restrictionsdiscourage their use in packaging applications. Indeed, in somecountries in the world, the use of styrofoam (trademark) is alreadyextremely limited by legislation. Biodegradable materials that areflexible, pliable and non-brittle are needed in a variety of packagingapplications, particularly for the manufacture of shaped biodegradablecontainers for food packaging. For such applications, the biodegradablematerial must have mechanical properties that allow it to be formed intoand hold the desired container shape, and be resistant to collapsing,tearing or breaking.

Starch is an abundant, inexpensive biodegradable polymer. A variety ofbiodegradable based materials have been proposed for use in packagingapplications. Conventional extrusion of these materials producesexpanded products that are brittle, sensitive to water and unsuitablefor preparation of packaging materials. Attempts to preparebiodegradable products with flexibility, pliability, resiliency, orother mechanical properties acceptable for various biodegradablepackaging applications have generally focused on chemical orphysio-chemical modification of starch, the use of expensive highamylose starch or mixing starch with synthetic polymers to achieve thedesired properties while retaining a degree of biodegradability. Anumber of references relate to extrusion and to injection molding ofstarch-containing compositions.

U.S. Pat. No. 5,397,834 provides biodegradable, thermoplasticcompositions made of the reaction product of a starch aldehyde withprotein. According to the disclosure, the resulting products formed withthe compositions possess a smooth, shiny texture, and a high level oftensile strength, elongation, and water resistance compared to articlesmade from native starch and protein. Suitable starches which may bemodified and used according to the invention include those derived, forexample, from corn including maize, waxy maize and high amylose corn;wheat including hard wheat, soft wheat and durum wheat; rice includingwaxy rice; and potato, rye, oat, barley, sorghum, millet, triticale,amaranth, and the like. The starch may be a normal starch (about 20-30wt-% amylose), a waxy starch (about 0-8 wt-% amylose), or a high-amylosestarch (greater than about 50 wt-% amylose).

U.S. Pat. Nos. 4,133,784, 4,337,181, 4,454,268, 5,322,866, 5,362,778,and 5,384,170 relate to starch-based films that are made by extrusion ofdestructurized or gelatinized starch combined with synthetic polymericmaterials. U.S. Pat. No. 5,322,866 specifically concerns a method ofmanufacture of biodegradable starch-containing blown films that includesa step of extrusion of a mixture of raw unprocessed starch, copolymersincluding polyvinyl alcohol, a nucleating agent and a plasticizer. Theprocess is said to eliminate the need of pre-processing the starch. U.S.Pat. No. 5,409,973 reports biodegradable compositions made by extrusionfrom destructurized starch and an ethylenevinyl acetate copolymer.

U.S. Pat. No. 5,087,650 relates to injection-molding of mixtures ofgraft polymers and starch to produce partially biodegradable productswith acceptable elasticity and water stability.

U.S. Pat. No. 5,258,430 relates to the production of biodegradablearticles from destructurized starch and chemically-modified polymers,including chemically-modified polyvinyl alcohol. The articles are saidto have improved biodegradability, but retain the mechanical propertiesof articles made from the polymer alone.

U.S. Pat. No. 5,292,782 relates to extruded or molded biodegradablearticles prepared from mixtures of starch, a thermoplastic polymer andcertain plasticizers.

U.S. Pat. No. 5,095,054 concerns methods of manufacturing shapedarticles from a mixture of destructurized starch and a polymer.

U.S. Pat. No. 4,125,495 relates to a process for manufacture of meattrays from biodegradable starch compositions. Starch granules arechemically modified, for example with a silicone reagent, blended withpolymer or copolymer and shaped to form a biodegradable shallow tray.

U.S. Pat. No. 4,673,438 relates to extrusion and injection molding ofstarch for the manufacture of capsules.

U.S. Pat. No. 5,427,614 also relates to a method of injection molding inwhich a non-modified starch is combined with a lubricant, texturingagent and a melt-flow accelerator.

U.S. Pat. No. 5,314,754 reports the production of shaped articles fromhigh amylose starch.

EP published application No. 712883 (published May 22, 1996) relates tobiodegradable, structured shaped products with good flexibility made byextruding starch having a defined large particle size (e.g., 400 to 1500microns). The application exemplifies the use of high amylose starch andchemically-modified high amylose starch.

U.S. Pat. No. 5,512,090 refers to an extrusion process for themanufacture of resilient, low density biodegradable packaging materials,including loose-fill materials, by extrusion of starch mixturescomprising polyvinyl alcohol (PVA) and other ingredients. The patentrefers to a minimum amount of about 5% by weight of PVA.

U.S. Pat. No. 5,186,990 reports a lightweight biodegradable packagingmaterial produced by extrusion of corn grit mixed with a binding agent(guar gum) and water. Corn grit is said to contain among othercomponents starch (76-80%), water (12.5-14%), protein (6.5-8%) and fat(0.5-1%). The patent teaches the use of generally known food extrudersof a screw-type that force product through an orifice or extensionopening. As the mixture exits the extruder via the flow plate or die,the super heated moisture in the mixture vaporizes forcing the materialto expand to its final shape and density.

U.S. Pat. No. 5,208,267 reports biodegradable, compressible andresilient starch-based packaging fillers with high volumes and lowweights. The products are formed by extrusion of a blend of non-modifiedstarch with polyalkylene glycol or certain derivatives thereof and abubble-nucleating agent, such as silicon dioxide.

U.S. Pat. No. 5,252,271 reports a biodegradable closed cell light weightloose-fill packaging material formed by extrusion of a modified starch.Non-modified starch is reacted in an extruder with certain mild acids inthe presence of water and a carbonate compound to generate CO₂.Resiliency of the product is said to be 60% to 85%, with density lessthan 0.032 g/cm³.

U.S. Pat. No. 3,137,592 relates to gelatinized starch products usefulfor coating applications produced by intense mechanical working ofstarch/plasticizer mixtures in an extruder. Related coating mixtures arereported in U.S. Pat. No. 5,032,337 which are manufactured by theextrusion of a mixture of starch and polyvinyl alcohol. Application ofthermomechanical treatment in an extruder is said to modify thesolubility properties of the resultant mixture which can then be used asa binding agent for coating paper.

Biodegradable material research has largely focused on particularcompositions in an attempt to achieve products that are flexible,pliable and non-brittle. The processes used to produce products fromthese compositions have in some instances, used extruders. For example,U.S. Pat. No. 5,660,900 discloses several extruder apparatuses forprocessing inorganically filled, starch-bound compositions. The extruderis used to prepare a moldable mixture which is then formed into adesired configuration by heated molds.

U. S. Pat. No. 3,734,672 discloses an extrusion die for extruding a cupshaped shell made from a dough. In particular, the die comprises anouter base having an extrusion orifice or slot which has a substantialhorizontal section and two upwardly extending sections which are slantedfrom the vertical. Further, a plurality of passage ways extend from therear of the die to the slot in the face of the die. The passage waychannels dough from the extruder through the extrusion orifice or slot.

Previously, in order to form clam shells, trays and other food productcontainers, biodegradable material was extruded as a flat sheet througha horizontal slit or linear extrusion orifice. The flat sheet ofbiodegradable material was then pressed between molds to form the clamshell, tray or other food package. However, these die configurationsproduced flat sheets of biodegradable material which were not uniformlythick, flexible, pliable and non-brittle. The packaging products moldedfrom the flat sheets also had these negative characteristics.

As the biodegradable material exited the extrusion orifice, thebiodegradable material typically had greater structural stability in adirection parallel to the extrusion flow direction compared to adirection transverse to the extrusion flow direction. In fact, fractureplanes or lines along which the sheet of biodegradable material waseasily broken, tended to form in the biodegradable sheet as it exitedfrom the extrusion orifice. Food packages which were molded from theextruded sheet, also tended to break or fracture along these planes.

Therefore, there is a need for a process which produces a flexible,pliable and non-brittle biodegradable material which has structuralstability in both the longitudinal and transverse directions

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided aextrusion die through which biodegradable material can be extruded whichhas structural stability in both the longitudinal and transversedirections of the material, which has a flow control device whichcontrols flow of biodegradable material through the extrusion die, andwhich allows the inner and outer walls of the extrusion orifice to beadjusted relative to each other to modify the circumferencial wallthickness of the cylindrical extrudate.

According to one embodiment of the invention, the die extrudes a tubularshaped structure which has its greatest structural stability in adirection which winds helically around the tubular structure. Thus, atthe top of the tubular structure, the direction of greatest stabilitytwists in one direction while at the bottom the direction of greateststability twists in the opposite direction. This tubular structure isthen pressed into a sheet comprised of two layers having theirdirections of greater stability approximately normal to each other. This2-ply sheet is a flexible, pliable and non-brittle sheet with strengthin all directions.

According to another embodiment of the present invention, the flow rateof the biodegradable material is regulated at a location upstream fromthe orifice and at the orifice itself to provide complete control ofextrusion parameters. In particular, the head pressure of thebiodegradable material behind the extrusion orifice is controlled toproduce an extrudate having desired characteristics.

According to a further embodiment of the invention, an annular extrusiondie allows the inner and outer walls of the extrusion orifice to beadjusted relative to each other to modify the circumferencial wallthickness of the cylindrical extrudate.

According to one aspect of the present invention, there is provided anextrusion die for extruding biodegradable material, the extrusion diecomprising: a mandrel; an outer member positioned near the mandrel; anextrusion orifice between the mandrel and the outer member; a member incommunication with at least one defining member of the extrusionorifice, wherein the member is capable of producing relative movementbetween the outer member and the mandrel, wherein the relative movementhas a component transverse to an extrusion direction of biodegradablematerial through the extrusion orifice; a flow control device whichcontrols flow of biodegradable material through the extrusion die; and apositioning device which positions the outer member and the mandrelrelative to each other.

According to another aspect of the invention, there is provided anextrusion die for extruding biodegradable material, the extrusion diecomprising: a cylindrical mandrel; a cylindrical outer ring positionedaround the mandrel; an annular extrusion orifice between the mandrel andthe outer ring; a member in communication with at least one definingmember of the annular extrusion orifice which produces angular relativemovement between the outer ring and the mandrel; a flow control devicewhich controls flow of biodegradable material through the extrusion die,wherein the flow control device comprises a mechanism which translatesthe outer ring to adjust the width of the annular extrusion orifice; anda positioning device which positions the outer ring and the mandrelrelative to each other.

According to a further aspect of the invention, there is provided anextrusion die for extruding biodegradable material the extrusion diecomprising: a mandrel; an outer member positioned near the mandrel; anextrusion orifice between the mandrel and the outer member, a mountingplate having a flow bore which conducts biodegradable material towardthe extrusion orifice, wherein the mandrel is fixedly mounted to themounting plate and the outer member is movably mounted to the mountingplate; a shearing member which moves the outer member relative to themandrel in a direction having a component transverse to an extrusiondirection of biodegradable material through the extrusion orifice; aflow control device which controls flow of biodegradable materialthrough the extrusion die, wherein the flow control device comprises aflow control channel upstream of the extrusion orifice, wherein the flowcontrol channel throttles flow of the biodegradable material through thedie, wherein the mandrel is attached to the mounting plate with at leastone spacer between, wherein the mounting plate and the mandrel definethe flow control channel; and a positioning device which positions theouter member and the mandrel relative to each other, wherein thepositioning device comprises a shifting device for moving the outermember and the mandrel relative to each other and a fixing device whichfixes the relative positions of the outer member and the mandrel.

According to another aspect of the invention, there is provided animproved process for the extrusion of biodegradable material wherein theextrusion comprises flowing the biodegradable material in a flowdirection through an orifice, the improvement comprising: moving orshearing the biodegradable material, in a direction having a componenttransverse to the flow direction, during extrusion; controlling the flowrate of biodegradable material through the extrusion die duringextrusion, wherein the controlling comprises adjusting the head pressureof the biodegradable material in the extrusion die and adjusting atleast one cross-sectional area of a biodegradable material flow pathwithin the extrusion die; and modifying the orifice geometry.

According to another aspect of the invention, there is provided aprocess for manufacturing biodegradable shaped products of increasedstrength, the process comprising: extruding a biodegradable material,wherein the extruding comprises moving the biodegradable material in afirst direction through an orifice to produce an extrudate; modifyingthe orifice geometry; shearing the biodegradable material, in a seconddirection having a component transverse to the first direction, duringthe extruding; controlling the flow rate of biodegradable materialthrough the extrusion die during the extruding, wherein the controllingcomprises adjusting the cross-sectional area of an extrusion orifice andwherein the controlling further comprises adjusting the cross-sectionalarea of a biodegradable material flow path at a location upstream of theextrusion orifice; compressing the extrudate; and molding the compressedextrudate of biodegradable material into a structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is better understood by reading the followingdescription of non-limitative embodiments, with reference to theattached drawings wherein like parts in each of the several figures areidentified by the same reference character, and which are brieflydescribed as follows.

FIG. 1 is a cross-sectional view of an embodiment of the invention fullyassembled.

FIG. 2 is a cross-sectional view of an embodiment of the die fullyassembled with centering and flow control devices.

FIG. 3 is an exploded perspective view of the several parts whichcomprise the die shown in FIG. 2.

FIG. 4 is a cross-sectional exploded view of a mandrel, mounting plateand spacers.

FIG. 5 is a cross-sectional exploded view of a gap adjusting ring, abearing housing and an end cap.

FIG. 6 is an exploded cross-sectional view of a seal ring, an outer ringand a die wheel.

FIG. 7A is a cross-sectional side view of an embodiment of the inventionhaving a motor and belt for rotating an outer ring about a mandrel.

FIG. 7B is an end view of the embodiment of the invention as shown inFIG. 7A.

FIG. 8 is a side view of a system for producing molded objects frombiodegradable material, the system comprising an extruder, a rotatingextrusion die, a cylindrical extrudate, rollers, and molding devices.

FIG. 9 is a flow chart of a process embodiment of the invention.

FIG. 10A is a perspective view of a cylindrical extrudate ofbiodegradable material having helical extrusion lines.

FIG. 10B is a perspective view of a sheet of biodegradable materialproduced from the extrudate shown in FIG. 10A.

FIG. 11 is an end view of an embodiment of the invention for rotatingthe die wheel of the rotating die, the device having a rack gear.

FIG. 12A is a perspective view of a cylindrical extrudate havingsinusoidal extrusion lines.

FIG. 12B is a top view of a sheet of biodegradable material producedfrom the extrudate shown in FIG. 12A.

FIG. 13 is an end view of a device for rotating the die wheel of anembodiment of the invention wherein the system comprises a worm gear.

FIG. 14A is a perspective view of an extrudate of biodegradable materialwherein the extrudate is cylindrical in shape and has zigzag extrusionlines.

FIG. 14B is a top view of a sheet of biodegradable material producedfrom the extrudate shown in FIG. 14A.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of the inventions scope, as the invention may admitto other equally effective embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a cross-section view of an embodiment of theinvention is shown. The die 1 is made up of several discrete annularmembers which share the same longitudinal central axis 3. A mountingplate 20 is located in the center of the die 1 and is the member towhich most of the remaining parts are attached. At one end of themounting plate 20, an extruder adapter 10 is attached for connecting thedie 1 to an extruder (not shown). A backplate 11 is attached between theextruder adapter 30 and the mounting plate 20. At an end opposite to theextruder adapter 10, several spacers 100 are positioned in counter sunkholes in the mounting plate 20 at various locations equidistant from thelongitudinal central axis 3. A mandrel 30 has counter sunk holes whichcorrespond to those in the mounting plate 20. The mandrel 30 is fixed tothe mounting plate 20 with the spacers 100 between, the spacers beinginserted into the respective counter sunk holes. On the same side of themounting plate 20 as the mandrel 30, a seal ring 40 is inserted into anannular spin channel 22 of the mounting plate 20. At the periphery ofthe mounting plate 20, the mounting plate 20 has a bearing portion 71which extends around the seal ring 40. An end cap 80 is attached to thedistal end of the bearing portion 71 of the mounting plate 20 to lockthe seal ring 40 in the spin channel 22. An outer ring 50 is attached tothe seal ring 40 around the outside of the mandrel 30 to form anextrusion orifice 5 between the outer ring 50 and the mandrel 30.Finally, a die wheel 90 is attached to the outer ring 50. As describedmore fully below, a motor and drive system drive the die wheel 90 torotate the outer ring 50 about the mandrel 30.

Biodegradable material is pushed through the die 1 under pressure by anextruder (not shown) which is attached to the extruder adapter 10. Thebiodegradable material passes through flow bore 23 which conducts thematerial through the extruder adapter 10 and the mounting plate 20 to acentral location at the backside of the mandrel 30. The biodegradablematerial is then forced radially outward through a disc-shaped cavitycalled a flow control channel 4 which is defined by the mounting plate20 and the mandrel 30. From the flow control channel 4, thebiodegradable material is pushed through the extrusion orifice 5 definedby the mandrel 30 and the outer ring 50. According to one embodiment ofthe invention, the biodegradable material is forced through theextrusion orifice 5, the die wheel 90, outer ring 50 and seal ring 40are rotated relative to the stationary mounting plate 20 and mandrel 30.

Referring to FIGS. 2 and 3, cross-sectional and exploded views,respectively, of an embodiment of the invention with orifice shiftingand flow control devices are shown. The die 1 is made up of severaldiscrete annular members which share the same longitudinal central axis3. A mounting plate 20 is located in the center of the die 1 and is themember to which most of the remaining parts are attached. At one end ofthe mounting plate 20, an extruder adapter is attached for connectingthe die 1 to an extruder (not shown). A gap adjusting ring 60 is placedconcentrically around the cylindrical exterior of the mounting plate 20.A bearing housing 70 lies adjacent the gap adjusting ring 60 and themounting plate 20. A seal ring 40 is placed within the bearing housing70 and is inserted into an annular spin channel of the mounting plate20. At an end opposite to the extruder adapter 10, several spacers 100are positioned in counter sunk holes in the mounting plate 20 at variouslocations equidistant from the longitudinal central axis 3. A mandrel 30has counter sunk holes which correspond to those in the mounting plate20. The mandrel is fixed to the mounting plate 20 with the spacers 100between. An outer ring 50 is attached to the seal ring 40 around theoutside of the mandrel 30 to form an extrusion orifice 5 between theouter ring 50 and the mandrel 30. Finally, a die wheel 90 is attached tothe outer ring 50 for rotating the outer ring 50 about the mandrel 30.

Referring to FIG. 4, a cross section of the mounting plate 20, spacers100 and the mandrel 30 are shown disassembled. The mounting plate 20 isbasically a solid cylinder with a cylindrical flow bore 23 cut in themiddle along the longitudinal central axis 3. One end of the mountingplate 20 comprises a mounting shoulder 21 for engagement with theextruder adapter 10 (shown in FIGS. 2 and 3). Opposite the mountingshoulder 21, the mounting plate 20 has a annular spin channel 22 forreceiving the seal ring 40 (shown in FIGS. 2 and 3). Between thecylindrical flow bore 23 at the center and the spin channel 22, themounting plate 20 has a disc-shaped flow surface 25. The mounting plate20 also has several mounting plate counter sunk holes 24 for receivingspacers 100 such that the counter sunk holes 24 are drilled in the flowsurface 25. In FIG. 4, only two counter sunk holes 24 are shown becausethe view is a cross section along a plane which intersects thelongitudinal central axis 3. All of the mounting plate counter sunkholes 24 are equidistant from each other and from the longitudinalcentral axis 3.

According to one embodiment of the invention, the mandrel 30 is a bowlshaped structure having a base 31 and sides 32. As shown in FIG. 4, themandrel 30 is oriented sideways so that the central axis of the mandrelis collinear with the longitudinal central axis 3 of the die. Unlike themounting, plate 20, which has a flow bore 23 through the center, themandrel 30 has a solid base 31. The outside surface of the base 31 is abase flow surface 33. The mandrel 30 has several countersunk holes 34which are cut in the base flow surface 33. In FIG. 4, only two mandrelcountersunk holes 34 are shown because the view is a cross-section alonga plane which intersects the longitudinal central axis 3. All of themandrel countersunk holes 34 are equidistant from each other and fromthe central axis 3. The inside of the mandrel 30 is hollowed out toreduce its overall weight.

Spacers 100 are used to mount the mandrel 30 to the mounting plate 20.Each of the spacers 100 comprise male ends 102 for insertion intomounting plate and mandrel countersunk holes 24 and 34. Of course, theoutside diameter of the male ends 102 is slightly smaller than theinside diameters of mounting plate and mandrel countersunk holes 24 and34. Between the male ends 102, each of the spacers 100 comprise a rib101 which has an outside diameter larger than the inside diameters ofthe mounting plate and mandrel countersunk holes 24 and 34. The rib 101of each spacer 100 has a uniform thickness in the longitudinal directionto serve as the spacer mechanism between the assembled mounting plateand mandrel.

The mandrel 30 is attached to the mounting plate 20 with mandrel bolts36. The mandrel bolts 36 extend through the base 31 of the mandrel 30,through the spacers 100 and into treaded portions in the bottom of themounting plate counter sunk holes 24. While the heads of the mandrelbolts 36 could be made to rest firmly against the inside of the base 31of the mandrel, in the embodiment shown, the mandrel bolts extendthrough risers 35 so that the heads of the mandrel bolts 36 are moreaccessible from the open end of the mandrel 30. In this embodiment, oneend of each of the risers 35 rests securely against the inside of themandrel base 31 while the other end of each riser is engaged by the headof a mandrel bolt 36.

Referring to FIG. 5, a cross-sectional view of the gap adjusting ring60, the bearing housing 70, and the end cap 80 are shown disassembled.The gap adjusting ring 60 is a ring shaped member having a longitudinalcentral axis 3 and an inner diameter slightly greater than the outsidediameter of the mounting plate 20 (shown in FIGS. 2 and 3). The gapadjusting ring 60 also has several lock screws 61 which extend throughan inner portion 62 of the gap adjusting ring 60 for engagement with themounting plate 20 once the gap adjusting ring 60 is placed around theoutside of the mounting plate 20. Also, the gap adjusting ring 60 has anouter portion 63 for engagement with the bearing housing 70. At theouter edge of the outer portion 63, the gap adjusting ring 60 hasshifting lugs 64 which are attached via lug bolts 65. In the embodimentshown, four shifting lugs 64 are attached to the outer portion 63 of thegap adjusting ring 60. The shifting lugs 64 are spaced around the gapadjusting ring 60 so that one is at the top, bottom, and sides,respectively. The shifting lugs 64 extend from the outer portion 63 in alongitudinal direction for positioning engagement with the bearinghousing 70. The shifting bolts 66 poke through the shifting lugs 64 inthe part of the shifting lugs 64 which extend from the outer portion 63in the longitudinal direction. The shifting bolts 66 poke through in adirection from outside the die toward the longitudinal central axis 3.Finally, the gap adjusting ring 60 has threaded holes 67 at variouslocations around the outer portion 63 for receiving screws 74.

The bearing housing 70 is an annular ring which has a longitudinalcentral axis 3. The bearing housing 70 has a bearing portion 71 and asupport portion 72. The support portion 72 is annular with is greatestcross-section in a direction transverse to the longitudinal central axis3. The bearing housing 70 is attachable to the gap adjusting ring 60 bythe support portion 72 which engages the outer portion 63 of the gapadjusting ring 60. In the embodiment shown, this engagement between thebearing housing 70 and the gap adjusting ring 60 is accomplished byscrews 74 between these two members. The support portion 72 has severalslip holes 75 which protrude through the support portion 72 in alongitudinal direction. In one embodiment, twelve slip holes 75 arepositioned equidistant from each other around the support portion 72 andare positioned equidistant from the longitudinal central axis 3. Theinside diameter of each slip hole 75 is larger than the outside diameterof screws 74 so that there is substantial “play” between the screws 74and the slip holes 75. While the slip holes 75 are larger than thescrews 74, the slip holes 75 are small enough so that the heads of thescrews 74 securely engage the support portion 72 of the bearing housing70.

The other major part of the bearing housing 70 is the bearing portion 71which is an annular section having its greatest thickness in thelongitudinal direction. The interior surface of the bearing portion 71is a bearing surface 76 for engaging lateral support bearings 42 (shownin FIG. 6). The bearing surface 76 supports the lateral support bearings42 in a plane normal to the longitudinal central axis 3. Protruding fromthe bearing surface 76 near the support portion 72, the bearing housing70 has a bearing housing lateral support flange 73 which supports alateral support bearing 42 of the seal ring 40 (shown in FIG. 6).

When the bearing housing 70 is attached to the gap adjusting ring 60,the relative positions of the two devices may be adjusted. Inparticular, during assembly, the shifting bolts 66 of the gap adjustingring 60 are relaxed to provide enough space for the support portion 72of the bearing housing 70. The bearing housing 70 is then placeddirectly adjacent the gap adjusting ring 60 with the support portion 72within the extended portions of shifting lugs 64. The screws 74 are theninserted through the slip holes 75 and loosely screwed into threadedholes 67 in the gap adjusting ring 60. The shifting bolts 66 are thenadjusted to collapse on the support portion 72 of the bearing housing70. The shifting bolts 66 may be adjusted to push the bearing housing 70off center relative to the gap adjusting ring 60. Because the slip holes75 are larger than the screws 74, the shifting bolts 66 freely push thebearing housing 70 in one direction or the other. By varying thepressure of the shifting bolts 66 against the outer surface of thebearing housing 70, the bearing housing 70, seal ring 40 and outer ring50 may be perturbed from their original positions to more desirablepositions. Once the desired relative position of the bearing housing 70to the gap adjusting ring 60 is obtained, the screws 74 are tightened tofirmly attach the two members.

The end cap 80 is preferably a ring which has a longitudinal centralaxis 3. The interior portion of the end cap 80 is a stabilizer 81 andthe exterior is a fastener flange 82. Fastener holes 83 are drilled inthe fastener flange 82 for inserting fasteners which secure the end cap80 to the bearing portion 71 of the bearing housing 70. The outsidediameter of the stabilizer 81 of the end cap 80 is slightly smaller thanthe inside diameter of the bearing portion 71 of the bearing housing 70.This allows the stabilizer 81 to be inserted into the bearing portion71. At the distal end of the stabilizer 81, there is an end cap lateralsupport flange 84 which supports a lateral support bearing 42 (shown inFIG. 6). Therefore, when the end cap 80 is securely fastened to thebearing housing 70, the bearing housing lateral support flange 73 andthe end cap lateral support flange 84 brace the lateral support bearings42 (shown in FIG. 6) against movement in the longitudinal directions.

Referring to FIG. 6, a cross-sectional view of the seal ring 40, theouter ring 50 and the die wheel 90 are shown disassembled. The seal ring40 is a cylindrical member having a longitudinal central axis 3. Theseal ring 40 has an interior diameter which decreases from one end tothe other. At the end of the seal ring 40 which has the smallest insidediameter, the seal ring 40 has a notch 47 for engaging the outer ring 50as discussed below. On the outside of the seal ring 40, there are foursuperior piston rings 41 for engaging the mounting plate 20 and the endcap 80 (both shown in FIGS. 2 and 3). The seal ring 40 also comprisestwo lateral support bearings 42. The lateral support bearings 42 areseparated by a bearing spacer flange 43 which is positioned between thetwo lateral support bearings 42. The seal ring 40 further comprises tworetaining rings 44 which are positioned on the outsides of the lateralsupport bearings 42. Thus, the seal ring 40 is assembled by slipping oneof the lateral support bearings 42 over each end of the seal ring 40until they are each adjacent opposite sides of the bearing spacer flange43. Next, retaining rings 44 are slipped over each end of the seal ring40 until they snap into grooves 45 at the outsides of the lateralsupport bearings 42. Thus, the lateral support bearings 42 are securedbetween the bearing spacer flange 43 and the retaining rings 44.Finally, the superior piston rings 41 are placed in piston slots 46.

The outer ring 50 is a cylindrical member having a longitudinal centralaxis 3. The outer ring 50 has a ring portion 51 and a fastener flange52. Longitudinal holes are cut through the fastener flange 52 forinserting fasteners which secure the outer ring 50 to an end of the sealring 40. The outside diameter of the ring portion 51 is slightly smallerthan the inside diameter of the notch 47 of the seal ring 40. Thisallows the outer ring 50 to be assembled to the seal ring 40 byinserting the ring portion 51 into the notch 47. The inside diameter ofthe ring portion 51 tapers from the end which attaches to the seal ring40 to the other. At the end of the ring portion 51 having the smallestinside diameter, the outer ring 50 comprises a lip 53 which defines oneside of the extrusion orifice 5 (shown in FIG. 2).

The die wheel 90 is a cylindrical member with a wheel flange 92 and adrive section 93. Holes are drilled through the wheel flange 92 forinserting wheel fasteners 91 which secure the die wheel 90 and the outerring 50 to the seal ring 40. The drive section 93 is a device whichengages a drive mechanism for rotating the die wheel 90. In theembodiment shown in the figure, the drive section is a pulley forengaging a drive belt.

Assembly of the complete die 1 is described with reference to FIGS. 2and 3. First, the extruder adapter 10 is secured to the mounting plate20 with a back plate 11 between. Next, with further reference to FIG. 4,several spacers 100 are placed in the mandrel 30 by inserting a male end102 of each spacer 100 into a mandrel counter sunk hole 34, until allthe mandrel counter sunk holes 34 have a spacer 100. The mandrel 30 isthen placed adjacent the mounting plate 20 with the protruding male ends102 of the spacers 100 being inserted into the mounting plate countersunk holes 24. The mandrel 30 is then attached to the mounting plate 20with spacers 100 between the mandrel bolts 36. In particular, the risers35 are slipped over the shanks of the mandrel bolts 36 and the mandrelbolts 36 are inserted through the mandrel base 31, the mandrel countersunk holes 34, the spacers 100, and the mounting plate counter sunkholes 24. The bottoms of the mounting plate counter sunk holes 24 arethreaded so that the mandrel bolts 36 may be screwed into the mountingplate 20. The mandrel bolts 36 are then screwed into the threadedbottoms of each mounting plate counter sunk hole 24 to fasten themandrel 30 to the mounting plate 20. With further reference to FIG. 5,the gap adjusting ring 60 is slipped over the exterior of the mountingplate 20. The lock screws 61 are then tightened against the exterior ofthe mounting plate 20. The bearing housing 70 is then positioned withthe support portion 72 against the outer portion 63 of the gap adjustingring 60. The shifting bolts 66 are adjusted to center the bearinghousing 70 about the longitudinal central axis 3 and the screws insertedthrough slip holes 75 and tightened into the threaded holes 67 of thegap adjusting ring 60. Next, with further reference to FIG. 6, the sealring 40 having superior piston rings 41, lateral support bearings 42 andretaining rings 44 attached thereto, is rotatably attached to thebearing housing 70. In particular, the seal ring 40 is inserted into thebearing housing 70 and then into the spin channel 22 of the mountingplate 20. The seal ring 40 is pushed all the way into the spin channel22 of the mounting plate 20 until the first of the lateral supportbearings 42 rests firmly against the bearing housing lateral supportflange 73. In this position, two of the four superior piston rings 41form a seal between the seal ring 40 and the spin channel 22 of themounting plate 20. The seal ring 40 is held in this position byinserting the stabilizer 81 of the end cap 80 into the bearing portion71 of the bearing housing 70. The end cap 80 is pushed all the way intothe bearing housing 70 until the end cap lateral support flange 84contacts the second of the lateral support bearings 42 of the seal ring40. Once in place, the end cap 80 is fixed to the bearing housing 70 byinserting fasteners through the fasteners holes 83 of the fastenerflange 82 and into the bearing portion 71 of the bearing housing 70. Theinterior surface of the stabilizer 81 of the end cap 80 engages theremaining two superior pistons rings 41 of the seal ring 40 so that theseal ring 40 is completely stabilized and allowed to spin freely aboutthe longitudinal central axis 3. With the end cap 80 securely fastenedto the bearing housing 70, the seal ring 40 is securely fastened in thelateral direction between the lateral support flanges 73 and 84. Withthe seal ring 40 securely in place, the outer ring 50 and die wheel 90are then attached to the end which protrudes from the mounting plate 20.In particular, the ring portion 51 of the outer ring 50 is inserted intothe notch 47 of the seal ring 40 and the wheel flange 91 of the diewheel 90 is positioned adjacent the fastener flange 52 of the outer ring50. Wheel fasteners 91 are then inserted through the wheel flange 92 andthe fastener flange 52 and locked into the seal ring 40.

Once assembled, both the extruder adapter 10 and the mounting plate 20further comprise a flow bore 23 which extends from the extruder (notshown) to the flow surface 25, as shown in FIGS. 2 and 4. Thus, the die1 operates such that biodegradable extrudate material is pushed by theextruder through the flow bore 23 until it reaches the base flow surface33 of the mandrel 30. The biodegradable extrudate then flows radiallyoutward around the spacers 100 between the flow surface 25 of themounting plate 20 and the base flow surface 33 of the mandrel 30. Thisdisc-like space between the mounting plate 20 and the mandrel 30 is theflow control channel 4. From the flow control channel 4, thebiodegradable extrudate then enters a cylindrical space between the sealring 40 and the mandrel 20 and is pushed through this space toward theextrusion orifice 5 between the mandrel 30 and the outer ring 50. As thebiodegradable extrudate moves toward the extrusion orifice 5, the diewheel 90 is rotated to rotate the outer ring 50 and seal ring 40 aroundthe stationary mandrel 30. Thus, the biodegradable extrudate is twistedby the rotating outer ring 50. As the extrudate exits the extrusionorifice 5, a tubular product of twisted biodegradable material isproduced. As described fully below, because the seal ring 40 isrotatably mounted within the bearing housing 70, the seal ring 40 may bemade to rotate about the mandrel 30 as the extrudate is pushed throughthe orifice 5.

Flow of the biodegradable material through the die 1 is controlled intwo ways: (1) adjusting the width of the flow control channel 4, and (2)controlling the size of the extrusion orifice 5. Regarding the flowcontrol channel 4, as noted above, biodegradable material is passed fromthe extruder through a flow bore 23 in the mounting plate 20 until itreaches the base flow surface 33 of the mandrel 30. From the centrallocation, the biodegradable material is pushed radially outward betweenthe base flow surface 33 of the mandrel 30 and the flow surface 25 ofthe mounting plate 20. Of course, as the biodegradable material flowsbetween the surfaces through the flow control channel 4, it passesaround each of the spacers 100 which separate the mandrel 30 and themounting plate 20. The width of the flow control channel 4 is adjustedby using spacers which have larger or smaller ribs 101 (See FIG. 4). Inparticular, if it is desirable to decrease flow of the biodegradablematerial through the flow control channel 4, spacers 100 having ribs 101which are relatively thin in the longitudinal direction are insertedbetween the mounting plate 20 and the mandrel 30. Alternatively, if itis desirable to increase a flow rate of biodegradable material throughthe flow control channel 4, spacers 100 having ribs 101 with relativelylarger thicknesses in the longitudinal direction are inserted betweenthe mounting plate 20 and the mandrel 30. Therefore, in a preferredembodiment, the die 1 has several sets of spacers 100 which may beplaced between the mounting plate 20 and the mandrel 30 to control thewidth of the flow control channel 4.

Additionally, flow of the biodegradable material through the extrusionorifice 5 is controlled by altering the width of the extrusion orifice5. The thickness of the extrusion orifice 5 between the mandrel lip 37and the outer ring lip 53 is adjusted by sliding the gap adjusting ring60, the bearing housing 70, the seal ring 40, and the outer ring 50along the longitudinal central axis 3 out away from the stationarymandrel 30. Since the interior diameter of the ring portion 51 of theouter ring 50 is tapered from the end which attaches to the seal ring40, the outer ring 50 has its smallest interior diameter at the outerring lip 53. To produce a biodegradable extrudate with a very thin wallthickness, the gap adjusting ring 60 is pushed all the way onto themounting plate 20 until the outer ring lip 53 is directly opposite themandrel lip 37. To produce a thicker biodegradable extrudate, the gapadjusting ring 60 is moved slightly away from the mounting plate 20along the longitudinal central axis 3 in the direction of directionarrow 6 (shown in FIG. 2), so that the outer ring lip 53 is positionedbeyond the mandrel lip 37. Thus, a wider section of the ring portion 51is adjacent the lip 37 of the mandrel 30 so that the extrusion orifice 5is thicker. Once the desired orifice size is obtained, lock screws 61are screwed into the gap adjusting ring 60 to re-engage the mountingplate 20, This locks the gap adjusting ring 60, the bearing housing 70,the seal ring 40, and the outer ring 50 in place to ensure the thicknessof the extrusion orifice 5 remains constant during operation. A thickerextrusion orifice 5 increases flow through the die.

Referring to FIGS. 7A and 7B, side and end views of portions of anembodiment of the invention for rotating the outer ring of the die areshown, respectively. The mandrel 30 is attached to the mounting plate 20so that the mandrel 30 is locked in place. The seal ring 40 and outerring 50 are rotatably mounted around the mandrel 30. A die wheel 90 isalso attached to the outer ring 50. All of these members havelongitudinal central axes which are collinear with longitudinal centralaxis 3. The device also has a motor 110 which has a drive axis 113 whichis parallel to longitudinal central axis 3. Attached to a drive shaft ofmotor 110, there is a drive wheel 111. The motor 110 and drive wheel 111are positioned so that drive wheel 111 lies in the same plane as the diewheel 90, the plane being perpendicular to the longitudinal central axis3. Opposite the drive wheel 111, the system further has a snubber wheel115 which is also positioned in the perpendicular plane of the drivewheel 111 and the die wheel 90. The snubber wheel 115 has a snubber axis116 which is also parallel to the longitudinal central axis 3. Thus, thedrive wheel 111 and the snubber wheel 115 are positioned at oppositeends of the system with the die wheel 90 between. A drive belt 112engages the drive wheel 111, the die wheel 90 and the snubber wheel 115.The snubber wheel 115 has no drive mechanism for turning the drive belt112. Rather, the snubber wheel 115 is an idle wheel which only turnswith the drive belt 112 when the drive belt 112 is driven by the motor110. The snubber wheel 115 serves only to evenly distribute forcesexerted by the drive belt 112 on the die wheel 90. Because the drivewheel 111 and snubber wheel 115 are positioned on opposite sides of thedie wheel 90, forces exerted by the drive belt 112 on the die wheel 90are approximately equal in all transverse directions. If the snubberwheel 115 were not placed in this position and the drive belt 112engaged only the drive wheel 111 and the die wheel 90, a net force wouldbe exerted by the drive belt 112 on the die wheel 90 in the direction ofthe motor 110. This force would pull the die wheel 90 and thus the outerring 50 out of center from its position about the stationary mandrel 30.Of course, this would have the detrimental effect of producing anextrudate tube of biodegradable material which would have a wallthickness greater on one side than on the other. Therefore, the snubberwheel 115 is positioned in the system to prevent the die wheel 90 frombeing pulled from its central location around the mandrel 30.

In a preferred embodiment, the drive belt 112 is a rubber belt.Alternatively, chains or mating gears may be used to mechanicallyconnect the motor 110 to the die wheel 90. A typical one-third horsepower electric motor is sufficient to produce the necessary torque todrive the drive belt 112. Further, the gear ratios between the drivewheel 111 and the die wheel 90 are such that the die wheel 90 maypreferably rotate at approximately 15 rotations per minute. Depending onthe particular gear system employed, alternative embodiments requiremore powerful motors.

Referring to FIGS. 8 and 9, system and method embodiments of theinvention are described for producing a biodegradable final product,respectively. The system 130 has a hopper 131 into which biodegradablematerial is initially placed (step 140). The hopper 131 supplies (step141) biodegradable material to an extruder 132 which pressurizes (step142) and cooks (step 143) the biodegradable material. The extruder 132pushes (step 144) the biodegradable material through an extrusion die 1.The extrusion die 1 is an embodiment of the rotating extrusion die ofthe present invention and is driven by a motor 110 with a drive belt1112. As the biodegradable material is pushed (step 144) through theextrusion die 1, an outer ring of the die 1 is rotated (step 145) aroundan inner mandrel. The biodegradable material is pushed (step 146) fromthe extrusion die 1 through an extrusion orifice to form a cylindricalextrudate 15. The cylindrical extrudate 15 is then pulled (step 147)from the extrusion orifice by a pair of press rollers 133. Next, thepress rollers 133 flatten (step 148) the cylindrical extrudate 15 into asheet 17 of biodegradable material. The sheet 17 of biodegradablematerial is then molded (step 149) between corresponding molds 134 toform the biodegradable material into final products. The shaped finalproducts are then deposited in bin 135.

According to alternative embodiments of the invention, it is desirableto stretch the cylindrical extrudate 15 as it exits the extrusionorifice 5. This is accomplished by rotating the press rollers 133slightly faster than a speed necessary to keep pace with the exit rateof the cylindrical extrudate 15 from the extrusion orifice 5. As thepress rollers 133 rotate faster, the cylindrical extrudate 15 is pulledby the press rollers 133 from the extrusion orifice 5 so that thecylindrical extrudate 15 is stretched in the longitudinal directionbefore it is flattened into a flat 2-ply sheet.

Referring to FIG. 10A, an example of a biodegradable extrudate from theextrusion die of the present invention is shown. The extrudate 15 exitsfrom the extrusion orifice 5 (see FIG. 2 for die components) as acylindrical structure. Typically, while not meant to be limited thereby,it is believed the polymer chains of the biodegradable material arealigned in the direction of extrusion to produce an extrudate which hasits greatest structural integrity in the extrusion direction. If theextrudate 15 exits the extrusion orifice 5 as the outer ring 50 isrotated around the mandrel 30, the extrudate 15 orients along extrusionlines 16.

Preferably, the cylindrical extrudate 15 is collapsed to form a sheet ofbiodegradable material having two extrudate layers. As shown in FIG.10B, a perspective view of a sheet of extrudate material produced fromthe tubular extrudate of FIG. 10A is shown. The sheet 17 is producedsimply by rolling the extrudate 15 through two rollers to compress thetubular extrudate 15 into the sheet 17. The sheet 17 consequentlycomprises extrusion lines 16 which form a cross-hatch pattern. The sheet17 is comprised of two layers, one of which previously formed one sideof the tubular extrudate 15 while the second layer of the sheet 17previously formed the other side of the extrudate 15. Therefore, becausethe extrusion lines 16 were helically wound around the extrudate 15,when the sheet 17 is formed, the extrusion lines 16 of the two layersrun in opposite directions. The extrusion line angle 18 of the extrusionlines 16 may be adjusted by controlling the flow rate of the extrudate15 from the extrusion orifice 5 of the die 1 (see FIG. 2 for diecomponents), and controlling the speed of angular rotation of the outerring 50 about the mandrel 30. If it is desirable to increase theextrusion line angle 18, the die is adjusted to increase the angularspeed of the outer ring 50 relative to the mandrel 30, and/or todecrease the flow rate of the extrusion material from the extrusion die.As noted above, the flow rate of the biodegradable material through thedie is controlled by adjusting the size of the extrusion orifice 5and/or the flow control channel 4.

According to one embodiment of the invention, the outer ring 50 of thedie 1 is made to rotate in both clockwise and counter-clockwisedirections about the mandrel 30 to produce a biodegradable extrudatewherein the extrusion lines have a wave pattern. To produce thisextrudate, the outer ring 50 is first rotated in one direction and thenrotated in the opposite direction. Depending on the rates of directionchange, the pattern produced is sinusoidal, zigzag, or boxed. Theperiods and amplitudes of these wave patterns are adjusted by alteringthe rate of rotation of the outer ring 50 and the flow rate of thebiodegradable material through the extrusion die 1.

Many different drive systems are available for alternating the directionof rotation of the outer ring 50. For example, the motor 110 of theembodiment shown in FIGS. 7A and 7B is made to alternate directions ofrotation. As the motor 110 changes directions of rotation, the drivewheel 111, drive belt 112 and die wheel 90 consequently changedirections.

Alternatively, as shown in FIG. 11, the die wheel 90 is a spur gear withradial teeth parallel to the longitudinal central axis 3. The teeth ofthe die wheel 90 are engaged by teeth of a rack gear 117. Opposite therack gear 117, an idler gear 124 is engaged with the die wheel 90 toprevent the rack gear 117 from pushing the outer ring 50 out ofalignment with the mandrel 30 (See FIG. 2). The rack gear 117 is mountedon a slide support 118 and moves linearly along a slide direction 120which is transverse to the longitudinal central axis 3. The slidesupport 118 is connected to a drive wheel 111 via a linkage 114. Inparticular, one end of the linkage 114 is connected to an end of theslide support 118 and the other end of the linkage 114 is connected tothe drive wheel 111 at its periphery. The slide support 118 is braced bybrackets 125 so that slide support 118 is only allowed to move alongslide direction 120. As the drive wheel 111 rotates clockwise aroundrotation direction 119, the linkage 114 pushes and pulls the slidesupport 118 back and forth along slide direction 120. The back and forthmovement of the slide support 118 rotates the die wheel 90 and the outerring 50 alternatively in clockwise and counterclockwise directions.

Since the linkage 114 is connected to the drive wheel 111 at itsperiphery, as noted above, the alternative clockwise andcounter-clockwise rotation of the outer ring 50 is a sinusoidaloscillatory type motion. Thus, this embodiment of the invention producesa biodegradable extrudate 15 with extrusion lines 16 which have a sinewave pattern as shown in FIG. 12A. As described above, the extrudate 15is rolled into a sheet 17 having two layers as shown in FIG. 12B. Theperiod of the sine waves are identified by reference character 19 andthe amplitude is identified by reference character 14. The period 19 andamplitude 14 of extrusion lines 16 may be adjusted by controlling theflow rate of the extrudate 15 from the extrusion orifice 5 of the die 1(see FIG. 2 for die components), and controlling the speed of angularrotation of the outer ring 50 about the mandrel 30. If it is desirableto increase the period of the sine waves, the die is adjusted todecrease the angular speed of the outer ring 50 relative to thestationary mandrel 30, and/or to increase the flow rate of the extrusionmaterial from the extrusion orifice 5. As noted above, the flow rate ofthe biodegradable material through the die is controlled by adjustingthe size of the extrusion orifice 5 and/or the flow control channel 4.Further, if it is desirable to increase the amplitude 14 of the sinewaves, the angular range of motion of the outer ring 50 is increased sothat the outer ring 50 rotates further around the stationary mandrel 30before it stops and changes direction. While many parameters may bealtered to produce this result, a simple modification is to use a drivewheel 111 which has a relatively larger diameter.

A similar embodiment of the invention which rotates the outer ring inclockwise and counter-clockwise directions is shown in FIG. 13. Asbefore, the die wheel 90 is a spur gear with radial teeth parallel tothe longitudinal central axis 3. The teeth of the die wheel 90 areengaged by teeth of a worm gear 122 which is positioned with its axis ofrotation transverse to the longitudinal central axis 3. Opposite theworm gear 122, an idler gear 124 is engaged with the die wheel 90 toprevent the worm gear 122 from pushing the outer ring 50 out ofalignment with the mandrel 30 (see FIG. 2). The worm gear 122 is drivenby a motor 110 with a transmission 121 between. A drive shaft 123 of themotor 110 is connected to a power side of the transmission 121 and theworm gear 122 is connected to a drive side of the transmission 121.While the motor 110 rotates the drive shaft 123 in only one direction,the transmission 121 rotates the worm gear 122 in both clockwise andcounter-clockwise directions. Further, in one embodiment, thetransmission 121 rotates the worm gear 122 at different speeds eventhough the motor 110 operates at only one speed. A similar embodimentcomprises a motor and transmission which drive a pinion gear whichengages the die wheel 90. Since the worm gear 122 is rotated at aconstant speed in each direction, this embodiment of the inventionproduces a biodegradable extrudate which has a zigzag pattern ofextrusion lines 16.

Since the motor 110 runs at constant angular velocity and thetransmission is used to change the direction of rotation of the wormgear 122, the alternative clockwise and counter-clockwise rotation ofthe outer ring 50 is an oscillatory type motion. Thus, this embodimentof the invention produces a biodegradable extrudate 15 with extrusionlines 16 which have a linear oscillatory wave pattern or zigzag wavepattern as shown in FIG. 14A. As described above, the extrudate 15 isrolled into a sheet 17 having two layers as shown in FIG. 14B. Theperiod of the zigzag waves are identified by reference character 19 andthe amplitude is identified by reference character 14. The period 19 andamplitude 14 of extrusion lines 16 is adjusted by controlling the flowrate of the extrudate 15 from the extrusion orifice 5 of the die 1 (seeFIG. 2 for die components), and controlling the speed of angularrotation of the outer ring 50 about the mandrel 30. If it is desirableto increase the period of the zigzag waves, the die is adjusted todecrease the angular speed of the outer ring 50 relative to thestationary mandrel 30, and/or to increase the flow rate of the extrusionmaterial from the extrusion orifice 5. As noted above, the flow rate ofthe biodegradable material through the die is controlled by adjustingthe size of the extrusion orifice 5 and/or the flow control channel 4.Further, if it is desirable to increase the amplitude 14 of the zigzagwaves, the angular range of motion of the outer ring 50 is increased sothat the outer ring 50 rotates further around the stationary mandrel 30before it stops and changes direction. While many parameters may bealtered to produce this result, a simple modification is to control thetransmission 121 to allow the worm gear 122 to run longer in eachdirection before reversing the direction.

While the particular embodiments for extrusion dies as herein shown anddisclosed in detail are fully capable of obtaining the objects andadvantages herein before stated, it is to be understood that they aremerely illustrative of the preferred embodiments of the invention andthat no limitations are intended by the details of construction ordesign herein shown other than as described in the appended claims.

LIST OF CHARACTER DESIGNATIONS

1. Die

3. Longitudinal Central Axis

4. Flow Control Channel

5. Extrusion Orifice

6. Direction Arrow

10. Extruder Adapter

11. Back Plate

14. Extrusion Wave Amplitude

15. Extrudate

16. Extrusion Lines

17. Sheet

18. Extrusion Line Angle

19. Extrusion Wave Period

20. Mounting Plate

21. Mounting Shoulder

22. Spin Channel

23. Flow Bore

24. Countersunk Holes

25. Flow Surface

30. Mandrel

31. Mandrel Base

32. Mandrel Sides

33. Base Flow Surface

34. Countersunk Holes

35. Risers

36. Mandrel Bolts

37. Mandrel Lip

40. Seal Ring

41. Superior Piston Rings

42. Lateral Support Bearings

43. Bearing Spacer Flange

44. Retaining Rings

45. Grooves

46. Piston Slots

47. Notch

50. Outer Ring

51. Ring Portion

52. Fastener Flange

53. Outer Ring Lip

55. Outer Die Structure

60. Gap Adjusting Ring

61. Lock Screws

62. Inner Portion

63. Outer Portion

64. Centering Lugs

65. Lug Bolts

66. Centering Bolts

67. Threaded Holes

70. Bearing Housing

71. Bearing Portion

72. Support Portion

73. Lateral Support Flange

74. Screws

75. Slip Holes

76. Bearing Surface

80. End Cap

81. Stabilizer

82. Fastener Flange

83. Fastener Holes

84. Lateral Support Flange

90. Die Wheel

91. Wheel Fastener

92. Wheel Flange

93. Drive Section

100. Spacer

101. Rib

102. Male Ends

110. Motor

11I. Drive Wheel

112. Drive Belt

113. Drive Axis

114. Linkage

115. Snubber Wheel

116. Snubber Axis

117. Rack Gear

118. Slide Support

119. Rotation Direction

120. Slide Direction

121. Transmission

122. Worn Gear

123. Drive Shaft

124. Idler Gear

125. Brackets

130. Biodegradable Product Producing System

131. Hopper

132. Extruder

133. Press Rollers

134. Molds

135. Bin

What is claimed is:
 1. An extrusion die for extruding biodegradablematerial, said extrusion die comprising: a cylindrical mandrel; acylindrical outer ring positioned around said mandrel; an annularextrusion orifice between said mandrel and said outer ring; and a memberin communication with at least one defining member of said annularextrusion orifice which produces angular relative movement between saidouter ring and said mandrel, wherein the relative movement has acomponent transverse to an extrusion direction of biodegradable materialthrough the extrusion orifice.
 2. An extrusion die as claimed in claim1, wherein said member reverses the direction of relative movementbetween said outer member and said mandrel.
 3. An extrusion die asclaimed in claim 1, further comprising a mounting plate having a flowbore which conducts biodegradable material toward said extrusionorifice, wherein said outer member is rotatably mounted to said mountingplate, and wherein said mandrel is fixedly mounted to said mountingplate.
 4. An extrusion die for extruding biodegradable material, saidextrusion die comprising: a mandrel; an outer member positioned aroundsaid mandrel; an extrusion orifice between said mandrel and said outermember; a mounting plate having a flow bore which conducts biodegradablematerial toward said extrusion orifice, wherein said mandrel is fixedlymounted to said mounting plate and said outer member is movably mountedto said mounting plate; and a member which moves said outer memberrelative to said mandrel in a direction having a component transverse toan extrusion direction of biodegradable material through the extrusionorifice.
 5. An extrusion die as claimed in claim 4, wherein said mandreland said outer member are cylindrical and wherein said member angularlyrotates said outer member around said mandrel and wherein said mandrelremains stationary.
 6. An extrusion die as claimed in claim 4, whereinsaid mandrel and said outer member are cylindrical and wherein saidmember angularly rotates said mandrel within said outer member andwherein said outer member remains stationary.
 7. An improved process forthe extrusion of biodegradable material wherein said extrusion comprisesflowing the biodegradable material in a flow direction through anannular orifice between a mandrel and an outer ring, said improvementcomprising: moving the biodegradable material, in a direction having acomponent transverse to the flow direction, during extrusion, whereinsaid moving comprises rotating an outer ring relative to a mandrel.
 8. Aprocess for manufacturing biodegradable shaped products of increasedstrength, said process comprising: extruding a biodegradable material,wherein said extruding comprises moving the biodegradable material in afirst direction through an annular orifice to produce a cylindricalextrudate, wherein the orifice is defined by a mandrel and an outer ringand wherein said shearing comprises rotating the outer ring relative tothe mandrel; shearing the biodegradable material, in a second directionhaving a component transverse to the first direction, during saidextruding; compressing the extrudate; and molding the compressedextrudate of biodegradable material into a structure.
 9. A process as inclaim 8, further comprising stretching the extrudate along the firstdirection before said compressing and said molding the extrudate.
 10. Anextrusion die for extruding biodegradable material, said extrusion diecomprising: a cylindrical mandrel; a cylindrical outer ring positionedaround said mandrel; an annular extrusion orifice between said mandreland said outer ring; a member in communication with at least onedefining member of said annular extrusion orifice which produces angularrelative movement between said outer ring and said mandrel; and a flowcontrol device which controls flow of biodegradable material through theextrusion die, wherein the flow control device comprises a mechanismwhich translates said outer ring to adjust the width of said annularextrusion orifice.
 11. An extrusion die as claimed in claim 10, furthercomprising a mounting plate having a flow bore which conductsbiodegradable material toward said annular extrusion orifice, whereinsaid outer member is rotatably mounted to said mounting plate, andwherein said mandrel is fixedly mounted to said mounting plate.
 12. Anextrusion die as in claim 10, wherein said flow control device comprisesa gap adjustment ring which adjusts the width of said annular extrusionorifice, wherein said gap adjustment ring adjusts the width of saidannular extrusion orifice by translating the outer member.
 13. Anextrusion die as in claim 10, wherein said flow control device comprisesa flow control channel which throttles flow of the biodegradablematerial through the die, and said extrusion die further comprises amounting plate and at least one spacer, wherein said mandrel is attachedto said mounting plate with said at least one spacer between, whereinsaid mounting plate and said mandrel define said flow control channel.14. An extrusion die for extruding biodegradable material, saidextrusion die comprising: a cylindrical mandrel; an outer memberpositioned around said mandrel; an extrusion orifice between saidmandrel and said outer member; a mounting plate having a flow bore whichconducts biodegradable material toward said extrusion orifice, whereinsaid mandrel is fixedly mounted to said mounting plate and said outermember is movably mounted to said mounting plate; and a member whichmoves said outer member relative to said mandrel in a direction having acomponent transverse to an extrusion direction of biodegradable materialthrough the extrusion orifice; a flow control device which controls flowof biodegradable material through the extrusion die, wherein said flowcontrol device comprises a flow control channel upstream of theextrusion orifice, wherein the flow control channel throttles flow ofthe biodegradable material through the die.
 15. An extrusion die asclaimed in claim 14, wherein said mandrel is attached to said mountingplate with said at least one spacer between, wherein said mounting plateand said mandrel define said flow control channel.
 16. An extrusion dieas claimed in claim 14, wherein said flow control channel is a discshaped cavity between said mandrel and said mounting plate, and whereinthe biodegradable material flows through the flow control channel from acentral location in the flow control channel outwardly to a peripherallocation in the flow control channel.
 17. An improved process forextruding biodegradable material wherein said extruding comprisesflowing the biodegradable material in a flow direction through anorifice, said improvement comprising: moving the biodegradable materialin a direction having a component transverse to the flow directionduring extruding; and controlling the flow rate of biodegradablematerial through the extrusion die during said extruding, wherein saidcontrolling comprises adjusting the head pressure of the biodegradablematerial in the extrusion die and adjusting at least one cross-sectionalarea of a biodegradable material flow path within the extrusion die. 18.A process as in claim 17, wherein said controlling comprises adjustingthe cross-sectional area of an extrusion orifice.
 19. A process as inclaim 17, wherein said controlling comprises adjusting thecross-sectional area of a biodegradable material flow path at a locationupstream of an extrusion orifice, wherein said controlling comprisesthrottling the biodegradable material through a flow control channel.20. A process for manufacturing biodegradable shaped products ofincreased strength, said process comprising: extruding a biodegradablematerial, wherein said extruding comprises moving the biodegradablematerial in a first direction through an annular extrusion orifice toproduce a cylindrical extrudate; moving the biodegradable material, in asecond direction having a component transverse to the first direction,during said extruding, wherein the orifice is defined by a mandrel andan outer ring and wherein said moving comprises rotating the outer ringrelative to the mandrel; controlling the flow rate of biodegradablematerial through the extrusion die during said extruding; compressingthe extrudate; and molding the compressed extrudate of biodegradablematerial into a structure.
 21. A process as in claim 20, wherein saidcontrolling the flow rate comprises adjusting the cross-sectional areaof the extrusion orifice, and wherein said adjusting comprisestranslating at least one wall of opposing walls of the extrusionorifice.
 22. A process as in claim 20, wherein said controlling the flowrate comprises adjusting the cross-sectional area of a biodegradablematerial flow path at a location upstream of the extrusion orifice, andwherein said adjusting the cross-sectional area of a biodegradablematerial flow path at a location upstream of the extrusion orificecomprises throttling the biodegradable material through a flow controlchannel.
 23. A process as in claim 20, further comprising stretching theextrudate along the first direction before said compressing and saidmolding the extrudate.
 24. An extrusion die for extruding biodegradablematerial for the manufacture of shaped articles, said extrusion diecomprising: a cylindrical mandrel; a cylindrical outer ring positionedaround said mandrel; an annular extrusion orifice between said mandreland said outer ring; a member in communication with at least onedefining member of said annular extrusion orifice which produces angularrelative movement between said outer ring and said mandrel; apositioning device which positions said outer ring and said mandrelrelative to each other, wherein said positioning device engages saidmounting plate, wherein said positioning device modifies a geometry ofsaid extrusion orifice; an apparatus for moving said positioning device;and an apparatus for fixing the position of said positioning device. 25.An extrusion die as claimed in claim 24, further comprising a mountingplate to which said mandrel is attached, wherein said apparatus formoving said positioning device comprises a lug and a bolt wherein saidlug is attached to said mounting plate, wherein said bolt is supportedby said lug, and wherein said bolt engages an outer die structure ofsaid positioning device.
 26. An extrusion die as claimed in claim 24,wherein said apparatus for moving said positioning device comprises aplurality of shifting apparatuses positioned equidistant from each otheraround said positioning device.
 27. An extrusion die as claimed in claim24, wherein said apparatus for fixing the position of said positioningdevice comprises a plurality of locking apparatuses positionedequidistant from each other around said positioning device.